Group policy not baing applied

hello friends,
i have set up a small network with windows 2000 server. i have set some group policies for members of an OU. The problem is that the policies (e.g., disabling display icon on the control panel) are not applied when a user of the OU logs on a machine. The user is a member of a security group for which the group policy is applied, and there is no other group policy of a parent organization or so overriding its policies. so i could not identify what actually has gone wrong!!

thanking u in advance,

ajay